Combustion Air Flow Requirements

Combustion air flow requirements will vary, depending on the specific engine model and rating. Specific air flow data for Caterpillar engines is given in both volumetric [m3/min (cfm)] and mass [kg/hr (lb/hr)] flow terms, at standard reference conditions.

Reference conditions for temperature and pressure are used to provide a basis for consistent measure of combustion air quantities. However, different parts of the world subscribe to different standards, thus it is important to note that the metric and English conditions are not equivalent. Caterpillar practice is to use ISO 8528 “normal” conditions of 25°C (77°F) and 101.3 kPaa (14.7 psia) when providing values in metric units, and ASME SAE J1349 “standard” conditions of 25°C (77°F) and 101.3 kPaa (14.7 psia) when providing values in English units.

To convert from mass airflow to volumetric airflow at reference conditions, use the following formula:

MR SR = QR

Where: MR = Mass air flow at reference conditions (kg/hr), (lb/hr) QR = Volumetric air flow at reference conditions (m3/min), (cfm) SR = Density of air at reference conditions (kg/m3), (lb/ft3). (Density of air = 1.292 kg/Nm3 (0.074 lb/ft3))

To convert both mass airflow and volumetric air flow from reference conditions to site conditions, use the following formulas:

MR x

TS TR = MS

QR x

TS TR = QS

Where: MR = Mass flow at reference conditions (kg/hr), (lb/hr). MS = Mass flow at site conditions (kg/hr), (lb/hr). QR = Air flow at reference conditions (m3/min), (cfm). QS = Air flow at site conditions (m3/min), (cfm). TR = Air temperature at reference conditions (°K), (°R). TS = Air temperature at site conditions (°K), (°R). °K = °C + 273. °R = °F + 460.